Stainless steel snap acting mechanism with low resistance electrical path

ABSTRACT

A snap acting electrical switch having a current carrying snap acting mechanism formed of an integral stainless steel member including a tension element and a compression element, one of the elements being substantially flat and the other being displaced from a planer configuration. The substantially flat element only having a material of higher conductivity joined thereto so as to enhance current carrying characteristics of the mechanism without having adverse effect on the mechanical characteristics of the mechanism.

United States Patent [151 3,674,969

Engle July 4, 1972 [54] STAINLESS STEEL SNAP ACTING 2,900,476 8/1959 Reece ..200/144 B MECHANISM WITH LOW RESISTANCE ELECTRICAL PATH Primary Examiner-H. 0. Jones Attorney-Lamont B. Koontz et a].

[72] Inventor: Gordon A. Engle, Freeport, Ill.

[73] Assignee: Honeywell Inc., Minneapolis, Minn. [57] ABSTRACT [22] Filed: 4, 1971 A snap acting electrical switch having a current carrying snap acting mechanism formed of an integral stainless steel PP'- N03 ,915 member including a tension element and a compression element, one of the elements being substantially flat and the 52 us. Cl. ..200/l66 c, 29/.630C other being displaced from a P configuration The 5 l lm. Cl. ..H0lh 1 02 Stamially flat element y having a material of higher conducsx Field of Search ..200/166 0, 144 B, 166 B0; tivily joined thereto 80 as to enhance current carrying charac- 29/630 C 'teristics of the mechanism without having adverse effect on the mechanical characteristics of the mechanism. 56 R l C! d I e erences I e 5 Claims, 3 Drawing Figures UNITED STATES PATENTS ,P'A'TENT'EDJuL4 1972 v INVENTOR GORDON A. ENGLE STAINLESS STEEL SNAP ACTING MECHANISM WITH LOW RESISTANCE ELECTRICAL PATH type which is formed of stainless steel so as to provide long mechanical life and which has a ribbon of material of higher conductivity joined to a discrete portion thereof to provide improved current carrying capacity.

Snap acting electrical switches of the general type disclosed in the Readeker US. Pat. No. 2,701,475 have been on the scene for a great number of years. Such switches can be constructed with snap acting mechanisms which provide excellent electrical and mechanical characteristics. Thus where the snap acting mechanism is formed of beryllium copper, it exhibits superior current carrying capacity and repeatability of actuating and de-actuating points. However, beryllium copper snap acting mechanisms are susceptible to corrosion, due to humidity, electrical arcing and the like, which can affect mechanical characteristics. Further, as with all electrical mechanical devices, such mechanisms have a finite electrical life. As is usually the case, work is constantly being done in an effort to find expedients which will retain the desirable features and overcome the shortcomings inherent in the beryllium copper approach. Thus it has been known for quite some time that snap acting mechanisms formed of stainless steel would provide switches with excellent corrosion resistant properties and outstanding mechanical life. However, stainless steel is a relatively poor electrical conductor and in those applications where the snap acting mechanism was to serve as a current carrying member such an approach to the problem was not usually satisfactory. To overcome the electrical conductivity shortcoming, it was suggested by British Pat. No. 669,969 to utilize snap acting mechanisms formed of stainless steel having an electrodeposited coating of copper or silver on the base material. This expedient obviously improves the current carrying capacity over stainless steel per so as is brought out in the patent but in turn this introduces another problem which affects mechanical characteristics. Thus the coating of the stainless steel snap acting mechanism adversely affects the spring characteristics of the mechanism in that an elasticity arises in portions of the mechanism.

I have discovered an approach whereby stainless steel can be utilized as the base material for a current carrying snap acting mechanism of an electric switch without sacrificing current carrying capacity and without adversely affecting mechanical characteristics of the mechanism. To bring this about, I join a ribbon of material of higher conductivity to a substantially fiat portion of the snap acting mechanism having stainless steel as the base material. The ribbon extends between the moving contact area and the fixed support or terminal area of the mechanism thereby enhancing the current carrying capacity of the mechanism. Since the flat portion and the associated ribbon does not experiencethe constant requirement of thrust of the remainder of the snap acting mechanism but rather initiates the overcenter action of the mechanism by a changing combination of tension with some bending, it is not subjected to the high shifting outer fiber stress that the thrust portion of the mechanism sees. Therefore, the ribbon can be of such a configuration so as to provide current carrying capacity comparable to that exhibited by a beryllium copper snap acting mechanism.

With my invention, which will be described in greater detail below, I have provided a snap acting mechanism that displays the long mechanical life and excellent operating characteristics identified with stainless steel along with the current carrying capacity identified with beryllium copper.

Therefore, it is an object of the present invention to provide a snap acting electrical switch including a current carrying snap acting mechanism formed of stainless steel having a material of higher conductivity disposed on a portion thereof so as to provide a device exhibiting long mechanical life as compared to beryllium copper and improved current carrying capacity as compared to stainless steel per se.

This and other objects will become apparent from a reading of the following specification and appended claims in which:

FIG. 1 is a perspective view of a snap acting member incorporating the invention;

FIG. 2 is a cross-section of a member of FIG. 1 taken along the FIG. 3 is a perspective cutaway cal switch incorporating the snap acting member of FIG. 1.

In FIG. 1 a snap acting spring member 10 generally of the form disclosed in the forementioned Readeker patent is shown. The spring member 10 includes a longer center element 12 having a through opening 14 at extremity 12a and a pair of shorter outer elements 16 all joined together at extremity 18 from which a contact 20 is supported.

The spring member 10 is formed of stainless steel preferably of the grade known in the trade as 301 although other grades may be equally satisfactory. In fabrication a portion of the center element 12 and extremity 18 of the stainless steel spring member 10 is removed, reference now being made to both FIG. 1 and 2, resulting in channel sections 12b and 18a in extremities 12a and 18, respectively, of the center element. A ribbon 22 of material having an electrical conductivity superior to stainless steel, preferably fine silver, is disposed over the area from which the portion of the stainless steel has been removed. The ribbon 22 is then secured to the stainless steel spring member 10 by difl usion bonding the adjacent surfaces together, as is well-known in the art. The resulting stainless steel spring member 10 and ribbon 22 combination is so formed that the thickness of the center element 12 with the ribbon in place is the same as the outer elements 16. I have found with a spring member as shown in FIG. 1 having overall dimensions of approximately 1.5 by 0.5 inches that utilizing a 0.00650.007 inch thick stainless steel stock and an in place ribbon 0.15 inch wide and 0.0012 inch thick provides a resulting combination for inclusion in an electrical switch which exhibits the superior electrical, environmental resistance and mechanical characteristics referred to above.

The spring member 10 of FIG. 1 is formed into a snap acting mechanism as shown in FIG. 3 where the center element 12 is secured in place in switch case 26 by means of fastener 28 passing through opening 14 and being upset against washer 30. Also secured in place under the spring member 10 by this expedient is U-shaped anchor member 32 which includes grooves 32a in which the extremities of outer elements 16 are pivotally supported. Contact 20 of the spring member 10 normally engages fixed contact 34 and upon snap over of the portion of the snap acting lines 2-2 thereof; and view of a snap acting electrispring member 10 engages lower fixed contact 36 both of which are appropriately secured to switch case 26.

As shown in FIG. 3, the snap acting mechanism formed by the spring member 10 includes a tension member comprised of the substantially flat center element 12 and two compression members comprised of the outer elements 16 which are displaced from a normal planer configuration to an installed arcuate position. With appropriate electrical connections made to the switch case 26 and specifically to fastener 28 and fixed contacts 34 and 36, electrical switching will take place upon snap over and return of the spring member 10. It will be noted that the ribbon 22 extends between the contact 20 and opening 14 of the spring member 10 and thus presents an electrical path of relatively low resistance between the electrical connections associated with the fastener 28 and fixed contacts 34 and 36.

To bring snap over and return aboutythe center element is moved by a plunger, not shown, located in a switch cover, not shown, in the vicinity of the area marked with an "X as is well-known in the art. During snap over and return, the center element 12 remains substantially flat. The ribbon 22 thus does not give rise to anelasticity and consequently does not adversely affect the spring" characteristics of the snap acting mechanism formed of the spring member 10 as it is located in a substantially inactive area of the spring" system.

By selectively locating a material of higher conductivity on a snap acting mechanism fon'ned of stainless steel, 1 have provided a patentably distinct advance which provides the electrica] characteristics normally associated with snap acting mechanisms fonned of conventional beryllium copper and the mechanical characteristics inherent in snap acting mechanisms formed of stainless steel.

My invention may of course take other forms in terms of 5 snap acting systems and ribbon materials, for example. Therefore, my contributions should be determined from the following claims.

lclaim:

l. A snap acting electrical switch including: a base member on which a pair of spaced stop portions are located, one of said stop portions being a fixed contact; and a snap acting mechanism formed of conductive strip material including integral first and second elements, discrete first extremities of said elements being assembled with support portions of said base member so as to place one of said elements in tension and the other of said elements in compression; one of said elements when in the assembled condition being substantially flat and remaining substantially fiat during actuation and de-actuation of said mechanism, the support portion for said flat element being a fixed terminal; the other of said elements when in the assembled condition having portions displaced from a planer configuration; said snap acting mechanism incorporating a moving contact portion proximate interconnected second extremities of said elements for movement between said pair of stop portions upon actuation and de-actuation of said mechanism; the improvement comprising said strip being formed of stainless steel and having a ribbon of material of higher conductivity joined to a surface of said flat element extending between the first extremity thereof and said moving contact so as to provide a lower resistance electrical path between said fixed contact, said moving contact, said ribbon of material and said fixed terminal.

2. The arrangement of claim 1 wherein said ribbon of material is diffusion bonded to the surface of said flat element.

3. The arrangement of claim 2 wherein said flat element is formed to include portions of reduced thickness with respect to the remainder of said mechanism, said ribbon of material associated with said portion of reduced thickness and being of such a thickness to provide a resulting combination having a thickness equal to that of the remainder of said mechanism.

4. The arrangement of claim 3 wherein the ribbon of material is fine silver.

5. The arrangement of claim 4 wherein the flat element is in tension. 

1. A snap acting electrical switch including: a base member on which a pair of spaced stop portions are located, one of said stop portions being a fixed contact; and a snap acting mechanism formed of conductive strip material including integral first and second elements, discrete first extremities of said elements being assembled with support portions of said base member so as to place one of said elements in tension and the other of said elements in compression; one of said elements when in the assembled condition being substantially flat and remaining substantially flat during actuation and de-actuation of said mechanism, the support portion for said flat element being a fixed terminal; the other of said elements when in the assembled condition having portions displaced from a planer configuration; said snap acting mechanism incorporating a moving contact portion proximate interconnected second extremities of said elements for movement between said pair of stop portions upon actuation and de-actuation of said mechanism; the improvement comprising said strip being formed of stainless steel and having a ribbon of material of higher conductivity joined to a surface of said flat element extending between the first extremity thereof and said moving contact so as to provide a lower resistance electrical path between said fixed contact, said moving contact, said ribbon of material and said fixed terminal.
 2. The arrangement of claim 1 wherein said ribbon of material is diffusion bonded to the surface of said flat element.
 3. The arrangement of claim 2 wherein said flat element is formed to include portions of reduced thickness with respect to the remainder of said mechanism, said ribbon of material associated with said portion of reduced thickness and being of such a thickness to provide a resulting combination having a thickneSs equal to that of the remainder of said mechanism.
 4. The arrangement of claim 3 wherein the ribbon of material is fine silver.
 5. The arrangement of claim 4 wherein the flat element is in tension. 